"What is real is not the external form but the essence of things. Starting from this truth it is impossible for anyone to express anything essentially real by imitating its exterior surface." —Constantin Brancusi
In the early 20th century, many avant-garde sculptors pushed the bounds of accepted modes of representation, abandoning faithfulness to the visible world in favor of abstraction. The question many artists asked was no longer how to reproduce the world as it appeared, but rather how to best express realities of life (sensed and theorized) through forms. Ever since, abstract sculpture has offered particularly fertile ground for experiments in shape, proportion, and technique, as well as for the embrace of non-traditional sculpting methods (apart from casting, welding, or direct carving), such as industrial manufacturing processes, plastic moulds, and even 3D printing. Modern strands of abstract sculpture include Concrete Art's mathematically precise and elegant forms, the strict geometry and forceful presence of Minimalist objects, and Kinetic Sculpture's embodiment of movement and physical forces.